Celebrate World Firefly Day by Keeping Nights Dark

Summer is in full swing in the northern hemisphere, and with it comes longer days, more outdoor adventures, and evenings spent outdoors with friends and family. For many of us, the arrival of summer is also synonymous with the arrival of fireflies. All across the central and eastern U.S. and Canada—and in small pockets of the West as well—fireflies can be seen performing their annual light show.

Watching and catching fireflies is a treasured childhood pastime for many of us. Fireflies have captured the human imagination for centuries and have frequently been the focus of art, literature, and cultural traditions. The spectacular courtship displays of some synchronous species (those that sync their flash patterns to occur at the same time) routinely draw huge crowds to firefly sanctuaries and parks in parts of Asia, Mexico, and the U.S. Even our non-synchronous species elicit awe and delight in viewers of all ages.

These cherished beetles are some of our most well-loved insects—yet their numbers appear to be dwindling. One likely driver for this decline is light pollution. Put simply, fireflies need dark nights.

Fireflies are part of cherished childhood memories for many people, but are unfortunately experiencing declines. Light pollution is likely contributing to this problem. (Photo: Benjamin Lehman / Flickr Creative Commons 2.0)

Bioluminescent species, which use various patterns of flashes and glows to communicate, can be outshone by bright lights from our cities, vehicles, and roadways. In fact, light pollution is impacting many species that are active at night (nocturnal) or at dusk (crepuscular)—not just bioluminescent creatures.

Light pollution comes in several forms, including skyglow (the glowing haze over highly populated areas), light trespass (light that reaches beyond its intended or needed area), and glare (light that excessively illuminates areas or objects). Together, these sources of artificial light at night are referred to as ALAN. Because of ALAN, night sky brightness is increasing worldwide, to the point that only a handful of areas in the U.S. and Canada are now truly dark at night. An astonishing 80% of people in North America can no longer see the Milky Way on even the clearest of nights, because it is obscured by skyglow from urban areas.

80% of people in North America can no longer see the Milky Way on even the clearest of nights, because it is obscured by skyglow from urban areas, as depicted in this photo of Salt Lake City. (Photo: makelessnoise / Flickr Creative Commons 2.0)

As our nights get brighter, animals that depend on darkness could suffer. ALAN can cause changes in animal behavior and affect species’ distribution, activity periods, and, ultimately, reproductive success. ALAN has already been identified as a threat to nocturnal pollination services, natural pest control, and seasonal migration patterns. More than 60% of invertebrate species are nocturnal, which means that many of these animals are likely to be impacted by ALAN. Fireflies are particularly at risk – more than 75% of the firefly species in the U.S. and Canada are nocturnal or dusk-active, and these species use bioluminescent light to communicate. ALAN can obscure this natural bioluminescence, interrupting signals used for mating and warding off predators.

In celebration of World Firefly Day (July 6-7) and in support of fireflies everywhere, we encourage you to consider the impact your lighting activities may have on our nighttime fauna. The theme of this year’s World Firefly Day is “Fireflies need dark nights.” Being thoughtful about outdoor lighting can benefit not only fireflies but also other nocturnal animals such as moths, bats, and sea turtles. The most important step to take to protect nocturnal species like fireflies from light pollution is to reduce or eliminate unnecessary outdoor lighting. For fireflies, this is especially important in the summer when adults are active. We can strive to keep as many areas as possible dark at night, while still keeping them safe for humans. Below are several other ways you can help provide the dark skies that fireflies need to thrive.

Recommendations to Help Fireflies:

• In areas where lights cannot be turned off at night, consider the following options:

◦ Swap bright light bulbs for dim red bulbs, which fireflies are less able to see, or filter existing bulbs to make them dimmer and redder.

◦ Limit outdoor illumination to desired areas such as sidewalks or pathways:

‣ Place landscape lighting low to the ground to reduce the lit area.

‣ Shield lights so they point down, rather than radiating outward in all 360 degrees.

‣ Use motion-detection and/or automatic timers so lights are on only as needed.

‣ Limit the number of hours per day that lights are kept on.

‣ Close your curtains or blinds at night when interior lights are on in order to reduce the amount of light that shines outside of your windows.

• Join or start a local chapter of the International Dark-Sky Association to advocate for local policies to control light pollution. In addition to helping fireflies and allowing people to appreciate the night sky, these initiatives often result in cost savings for municipalities and businesses—everyone can win!

• Another way to contribute to firefly conservation is to participate in community science dedicated to understanding the distribution and population trends of our many firefly species. Two programs we recommend checking out are Firefly Watch, a nationwide program run by Mass Audubon, and the Western Firefly Project, a western-focused project run by the Utah Natural History Museum.

• And don’t forget to visit the Fireflyer’s International Network to share and view events and other activities happening across the world in celebration of World Firefly Day.

Written by Candace Fallon, Xerces Society Senior Endangered Species Conservation Biologist and Public Lands Lead.